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Articles on Trending Technologies
Technical articles with clear explanations and examples
Getting File Information in Perl
You can test certain features very quickly within Perl using a series of test operators known collectively as -X tests. For example, to perform a quick test of the various permissions on a file, you might use a script like this −#/usr/bin/perl my $file = "/usr/test/file1.txt"; my (@description, $size); if (-e $file) { push @description, 'binary' if (-B _); push @description, 'a socket' if (-S _); push @description, 'a text file' if (-T _); push @description, 'a block special file' if (-b _); push @description, 'a character special file' if (-c _); push @description, ...
Read MorePositioning inside a File in Perl
You can use to tell function in Perl to know the current position of a file and seek function to point a particular position inside the file.Perl tell FunctionThe first requirement is to find your position within a file, which you do using the tell function −tell FILEHANDLE tellThis returns the position of the file pointer, in bytes, within FILEHANDLE if specified, or the current default selected filehandle if none is specified.Perl seek FunctionThe seek function positions the file pointer to the specified number of bytes within a file −seek FILEHANDLE, POSITION, WHENCEThe function uses the fseek system function, and you have ...
Read MoreCopy, Rename and Delete Files in Perl
Here is the Perl example, which opens an existing file file1.txt and read it line by line and generate another copy file file2.txt.#!/usr/bin/perl # Open file to read open(DATA1, "file2.txt"); # Copy data from one file to another. while() { print DATA2 $_; } close( DATA1 ); close( DATA2 );Renaming a fileHere is the Perl example, which shows how we can rename a file file1.txt to file2.txt. Assuming file is available in /usr/test directory.#!/usr/bin/perl rename ("/usr/test/file1.txt", "/usr/test/file2.txt" );This function renames takes two arguments and it just renames the existing file.Deleting an Existing FileHere is an example, which shows how ...
Read MoreReading and Writing Files in Perl
Once you have an open file handle in Perl, you need to be able to read and write information. There are a number of different ways of reading and writing data into the file.The OperatorThe main method of reading the information from an open filehandle is the operator. In a scalar context, it returns a single line from the filehandle. For example −#!/usr/bin/perl print "What is your name?"; $name = ; print "Hello $name";When you use the operator in a list context, it returns a list of lines from the specified filehandle. For example, to import all ...
Read MoreOpening and Closing Files in Perl
There are following two functions with multiple forms, which can be used to open any new or existing file in Perl.open FILEHANDLE, EXPR open FILEHANDLE sysopen FILEHANDLE, FILENAME, MODE, PERMS sysopen FILEHANDLE, FILENAME, MODEHere FILEHANDLE is the file handle returned by the open function and EXPR is the expression having file name and mode of opening the file.Open FunctionFollowing is the syntax to open file.txt in read-only mode. Here less than < sign indicates that file has to be opened in read-only mode.open(DATA, ">file.txt") || die "Couldn't open file file.txt, $!";A double >> opens the file for appending, placing the file pointer ...
Read MoreDefine a Report Footer in Perl
While $^ or $FORMAT_TOP_NAME contains the name of the current header format in Perl, there is no corresponding mechanism to automatically do the same thing for a footer. If you have a fixed-size footer, you can get footers by checking variable $- or $FORMAT_LINES_LEFT before each write() and print the footer yourself if necessary using another format defined as follows −format EMPLOYEE_BOTTOM = End of Page @< $% .For a complete set of variables related to formatting, please refer to the Perl Special Variables section.
Read MoreDefine a Pagination in Perl
What about if your report is taking more than one page? You have a good solution in Perl to create pagination. We simply use $% or $FORMAT_PAGE_NUMBER variable along with header as follows −format EMPLOYEE_TOP = =================================== Name Age Page @< $% =================================== .Now your output will look like as follows −=================================== Name Age Page 1 =================================== =================================== Ali 20 2000.00 =================================== =================================== Raza 30 2500.00 =================================== =================================== Jaffer 40 4000.00 ===================================
Read MoreCreate References in Perl
A Perl reference is a scalar data type that holds the location of another value which could be scalar, arrays, or hashes. Because of its scalar nature, a reference can be used anywhere, a scalar can be used.It is easy to create a reference for any variable, subroutine or value by prefixing it with a backslash as follows −$scalarref = \$foo; $arrayref = \@ARGV; $hashref = \%ENV; $coderef = \&handler; $globref = \*foo;You cannot create a reference on an I/O handle (filehandle or dirhandle) using the backslash operator but a reference to an anonymous array can be created using the ...
Read MoreSubroutine Call Context in Perl
The context of a Perl subroutine or statement is defined as the type of return value that is expected. This allows you to use a single function that returns different values based on what the user is expecting to receive. For example, the following localtime() returns a string when it is called in scalar context, but it returns a list when it is called in list context.my $datestring = localtime( time );In this example, the value of $timestr is now a string made up of the current date and time, for example, Thu Nov 30 15:21:33 2000. Conversely −($sec, $min, ...
Read MorePerl Operators Precedence
The following table lists all operators from highest precedence to lowest in Perl Programming.
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